Field of the Invention
The present invention relates to a method for preparing a polymer and a use of the polymer, and belongs to the technical field of concrete admixtures.
Description of Related Art
With rapid economic growth in China, the usage amount of concrete increases on the order of tenths of a percent per year, and meanwhile, the technical level of concrete applications is also growing. Among numerous concrete admixtures, a water-reducing agent is one of admixtures that are most widely researched and applied. The water-reducing agent is a surfactant in nature, and is mainly used to improve the flowability of concrete, control the setting or hardening time, and increase the strength of concrete.
A polycarboxylic acid water-reducing agent is a high-performance water-reducing agent, which molecular structure is formed mainly by free radical polymerization of a polyether macromonomer and an unsaturated carboxylic acid molecule. Electrostatic repulsion may occur between carboxylic acid functional groups and a strong steric effect may occur in side chains, so that the carboxylic acid water-reducing agent has higher water-reducing efficiency compared to early water-reducing agents. With wide applications of the carboxylic acid water-reducing agent, improvements in performance thereof are increasingly reported.
A patent document U.S. Pat. No. 5,393,343A introduces a polyoxyalkyleneamine polyether, which may be subjected to amidation with polyacrylic acid to obtain a corresponding polycarboxylic acid water-reducing agent. Such a water-reducing agent has good slump-retaining property. The disadvantage of this method is that a large amount of an organic solvent is required to remove water generated during the reaction, and the product has low solubility in water, so that practical limitations are greatly limited.
A patent document CN1096774A discloses a polycarboxylic acid water-reducing agent for controlling slump loss in concrete. This composition is formed by polymerization of alkenyl ether, dialkenyl ether and maleic anhydride as monomers with azobisisobutyronitrile as an initiator system in a solvent toluene. Although the water-reducing agent in this invention has high slump-retaining properties, the disadvantages are that the water-reducing properties are slightly poor, the required dosage is relatively high, the production process is environmentally unfriendly, and the used raw material alkenyl ether is expensive.
While polycarboxylic acid water-reducing agents have made significant advances in water-reducing and slump-retaining properties, there are two pronounced problems occurring in use. On the one hand, a polycarboxylic acid water-reducing agent molecule itself has high air-entraining effect, resulting in potential great impact on later strength improvement of concrete. In order to address the problem of too high air-entraining effect of the polycarboxylic acid water-reducing agent, it has been reported in patent documents EP601536A1 and EP1138697A1 that a small amount of an anti-foaming agent may be added, so as to substantially decrease the air content in a short term. However, after long-term storage, the problem of poor compatibility may occur, thus resulting in decrease in anti-foaming ability.
A patent document U.S. Pat. No. 6,803,396B2 introduces an anti-foaming agent that is ethylene oxide-propylene oxide block polyether capped with primary amine functional groups. The principle is that the problem of poor compatibility is solved with interaction between primary amine groups and carboxylic acid functional groups. However, it is to be noted that such a polyether is expensive and commercial mass production therefor is difficult.
On the other hand, the polycarboxylic acid water-reducing agent suffers from the problem of poor adaptability for clays. The polycarboxylic acid water-reducing agent has strong adsorption tendency in clays and minerals, and is highly sensitive to the mud content of aggregates, which greatly affects transportation, operating state and strength of concrete. Currently, there are no good solutions for the problem of poor adaptability for clays, and only some combinations of small molecules such as sodium gluconate, sucrose, citric acid, potassium salts, and the like are used to improve the nature of concrete, which cannot fundamentally solve the problem of poor adaptability of polycarboxylic acid water-reducing agents in a region having a high mud content.